Embodiments of the present invention relate to Near Field Communications cards (NFC cards), and more particularly to NFC cards intended to be inserted within a handheld device such as a mobile telephone. Embodiments of the present invention also relate to a method for performing a contactless communication between an NFC card and an external NFC device.
Known NFC cards intended to be inserted within handheld devices are for example NFC Subscriber Identity Modules, also called SIM-NFC, or NFC Secure Digital (SD) cards. International Publication WO 98/58509 discloses a SIM-NFC card including contact pads, a microprocessor, an NFC module, and an antenna coil. The antenna coil has one or more coplanar coaxial windings parallel to the plane of the card, and therefore presents a magnetic axis perpendicular to the plane of the card. It can perform contact communications with the mobile telephone through the contact pads and an NFC communication with an external NFC device through the antenna coil.
When the card and the external NFC device are placed sufficiently close to each other, the antenna coil of the card is inductively coupled to an antenna coil of the external NFC device, and data can be exchanged using conventional NFC techniques such as those defined by standards ISO 14443, ISO 15693, and Sony Felica.
In most applications, the external device emits a magnetic field while the NFC card is passive and sends data by load modulation. To that end, the antenna coil of the card is associated with passive components (e.g. capacitors) to form an antenna circuit tuned to a working frequency of the external device, for example 13.56 MHz.
Handheld devices often contain metal parts or metal components. When an NFC card is inserted in a handheld device, such metal parts or components reduce the inductance of the antenna coil, thereby altering the tuning frequency of the antenna circuit and reducing the maximum communication distance between the NFC card and the external device.
It is difficult for NFC card manufacturers to know in advance in what conditions an NFC card will be used, that is, what will be the metallic environment of the card. The location for the card may vary widely from handheld device to handheld device. The location may be more or less electromagnetically shielded, and the handheld device may include a variable number of metal parts that are close to the card. Consequently, the maximum communication distance of the card depends heavily on the environment around the card and may vary greatly depending on the handheld device within which the card is inserted.
Additionally, handheld devices are sometimes designed so that the NFC cards are placed underneath their battery, which may be the case, for example, when the connector receiving the card is mounted on the main printed circuit board of the handheld device (mother board). In this case, the battery may extend over the antenna coil and cross its magnetic axis. Consequently, the maximum communication distance is further diminished such that contactless communications become impossible or only possible with a very short communication distance.
In addition, the magnetic field emitted by external device induces eddy currents in the metal parts, which create a counter magnetic field that tends to neutralize the magnetic field, thereby reducing even more the maximum communication distance between the NFC card and the external device.
It may therefore be desired to provide an NFC card that offers a maximum communication distance less dependent on the environment surrounding the card, when the card is inserted in a handheld device.